Known in the art is a method of detection of communication errors over a network by using monitoring devices. In such a detection method, for example, a plurality of monitoring devices which detect communication errors send and receive data and judge deterioration of the quality of data to thereby determine the links of the network at which errors occur. Note that, a “link” means a physical connection between components of a network.
The plurality of monitoring devices are arranged in the network to communicate test data between them and judge degradation of quality of data. Below, such communication of test data will be referred to as “inspection flows”. However, the inspection flows between the plurality of monitoring devices pass through pluralities of links, so with a single inspection flow, while it might be learned that there is an error in one link through which the inspection flow passes, it is not possible to identify the link at which the degradation of quality of data occurred. A plurality of monitoring devices which differ in transmission locations and reception locations run inspection flows over the network so as to pass a link number of times. Thus, it is possible to identify a link at which degradation of quality of data occurred.
Further, when the number of inspection flows is not sufficient for the total number of links of a network, sometimes it is not possible to determine a failure link among the links through which inspection flows pass. For this reason, the method has been proposed of identifying the inspection flows which are required for identifying a failure link on a network.
As related art, there is the technical report of the Institute of Electronics, Information and Communication Engineers “Estimating points of QoS degradation in the network from the aggregation of per-flow quality information”, March 2005, pp. 31 to 36.